1. Field of the Invention
The present invention relates to an improved process for the hydroformylation of olefinically unsaturated compounds. The invention also relates to an installation for carrying out the said process.
The hydroformylation of olefinic compounds is a reaction of great industrial importance, and the majority of processes utilize homogeneous catalysts dissolved in an organic phase made up of the reagents, the products and, where appropriate, an excess of ligand, with the result that difficulties are encountered in separating off and recovering the catalyst, in particular if this is employed in a relatively large amount, as is the case with catalysts based on cobalt, or if this is a noble metal, as is the case with catalysts based on rhodium.
2. Description of the Prior Art
One solution aimed at solving this problem has been mentioned by Bartik et al.: Organometallics (1993) 12 164-170, J. Organometal. Chem. (1994) 480 15-21 and by Beller et al.: J. Molecular Catal. A: Chemical (1999) 143 31-39. It consists of carrying out the hydroformylation in the presence of an aqueous solution comprising a cobalt complex which is rendered water-soluble due to the presence of a phosphine-sulfonate ligand, such as the sodium salt of trisulfonated triphenylphosphine or of a trisulfonated tris-(alkylphenyl)-phosphine. The Patent Application WO-A-97/00132 describes cobalt clusters substituted by trialkoxysilylmethyl groups, which renders them soluble in water. In this manner, the organic phase containing the aldehydes is easily separated from the aqueous phase containing the catalyst.
Another solution aimed at solving this problem has been described in French Patent No. 2,314,910. It consists of carrying out the hydroformylation in the presence of an aqueous solution comprising a rhodium complex which is rendered water-soluble due to the presence of a sulfonated phosphine ligand which is itself water-soluble, such as the sodium salt of trisulfonated triphenylphosphine. In this manner, the organic phase containing the aldehydes is easily separated from the aqueous phase containing the catalyst. This technique has been the subject of a considerable number of works which have been discussed in an article by W. A. Hermann published in Angewandte Chemie International in 1993, volume 32, page 1524 et seq.
In spite of a great industrial interest in these techniques for the hydroformylation of propylene, these two-phase systems suffer from the lack of solubility of olefins in water, which leads to relatively low reaction rates, rendering them impracticable for long-chain olefins.
Furthermore, the U.S. Pat. No. 3,565,823 has described a technique consisting of dispersing a transition metal compound in a quaternary ammonium or phosphonium salt of tin or germanium of the formula (R1R2R3R4Z)YX3, in which R1, R2, R3 and R4 are hydrocarbon radicals having up to 18 carbon atoms, Z is nitrogen or phosphorus, Y is tin or germanium and X is a halogen, for example chlorine or bromine. The patent U.S. Pat. No. 3,832,391 has described a process for the carbonylation of olefins by the same composition. The above compositions have the disadvantage of having a relatively high melting point, for example above 90xc2x0 C., which complicates handling of solutions of the catalyst and reaction products.
It has been indicated in U.S. Pat. No. 5,874,638 that it is possible to benefit from the advantages of using two phases while at the same time limiting the disadvantages associated on the one hand with the use of water and on the other hand with the use of compounds of high melting point by dissolving certain catalytic compounds of transition metals of groups 8, 9 and 10 of the periodic table, which are known to catalyse hydroformylation, in non-aqueous ionic solvents comprising organic-inorganic salts which are liquid at ambient temperature.
It has now been found that it was possible to increase the rates of reaction considerably by carrying out the reaction in an ionic liquid which is partly or completely miscible with the reaction products, while preserving the benefit of separating off and re-using the ionic liquid containing the catalyst and improving the yield of the reaction products by injecting, after the reaction section, an organic solvent (which can advantageously be the olefinically unsaturated compound to be hydroformylated) which is of low miscibility or immiscible with the ionic liquid and which improves demixing of the products from the remainder of the reaction effluent.
This process procedure allows the advantages of a homogeneous catalytic system to be combined with providing better utilization of the catalyst and a better yield of the products.